In an electric opening and closing drive mechanism for a power window in an automobile, in general, the rotation from a motor is smoothly transmitted to an arm with any shock absorbed, and a gear complete is used for buffering vertical looseness. In manufacturing this type of part, an annular rubber member is stoved, by a vulcanization-forming or molding, between upper and lower disks with an adhesive applied to said disks, thereby providing an integrally-formed part.
In such a vulcanization-forming, a rubber and a metal may be reliably adhesively bonded by a rubber-vulcanizing reaction coinciding in timing with a reaction of a metal plate and the adhesive. Therefore, a failure of adhesion may be produced in some cases with an inferior timing between the rubber-vulcanizing reaction and the reaction of the metal plate and the adhesive in a process of mass production of such parts.
The failure of adhesion may be also produced due to inadequate application of adhesive, an excessive thermal treatment in an adhesive drying step, adhesion of a release agent on a bonded surface, adhesion of a material disturbing the adhesion properties such as fats and oils, and the like.
Thereupon, the following methods have conventionally been adopted: a method for estimating the failure of adhesion for a population of formed products by picking up a small number of parts from the population and subjecting them to an adhesion rupture test in which a thrust force is applied between the rubber member and the metal disk; and a method for examining the failure of adhesion by applying, to all of products, a stress as low as not to exert any practical influence without providing any damage.
In the above rupture test involving the picking-up, however, the adhesion properties of all the products are not necessarily assured. On the other hand, in the method for estimation by applying the low stress, the products whose parts have been slightly adhesively bonded can be estimated, but if the parts have been adhesively bonded by a stronger adhesive force than the low stress applied for estimating, then it is impossible to detect a possibility of a failure of adhesion for products in which components are bonded somewhat but with an incomplete adhesion and hence, adhesion-defective products have often flowed into the market.